Polytetrafluoroethylene suction box cover for fourdrinier machines



March 10, 1959 R. L. HOLMES 2,876,685 POLYTETRAFLUOROETHYLENE SUCTION BOX COVER FOR FOURDRINIER MACHINES Filed Aug. 15, 1957 i m i i /a I F :1? ,6 20 i /9 F 3 INVENTOR.

nrrapms-ys United States Patent l"OLY 'I'ETRAFLU0RO12;'II-IYLENE". SUCTION- BOX COVER FOR FOURDRINIER MACHINES Robert L. Holmes, North..Cliarleston, S. (3., assiguor. to

Raybestos-Manhattan, Inc., Passaic, N. J., a corporation ofNewJei-sey Application August 15., 1957', Serial No. 678,398

4 Claims. (GI; 92-51) This invention relates to an improved suction box cover for Fourdrinier paper making, machines.

The. prime objectv of' the present invention'centers about the provision of a suction box coverfor Fourdrinier machines which accomplishes the dual purpose of reducing the wear on and, therefore, increasing the operating life of both thescreemwire whichismoved at speed over the suction, boxcover and the, suction box cover itself.

Of the several types of machines used in making the paper,. the Fourdrinier machine produces paper at the fastest rate and inthe greatest tonnagesper day. Modern machines of thistype. are run atxa. speed of 2000 to 2200 feet per minute and some. are being erected to be run from 25.00 to 3000-feet per minute, the high. speed being desired for producing paper quicklyand at. a lower cost; This: increased, and everincreasing, speed, however, has produced. and produces, problems relating. to the wear of the machine parts.

As is known, in the Fourdrinier machine, a slurry of wood pulp fibres in water is fedevenlytoa movable wire screen, the Wire: screen being used to permit the water to drain or be sucked out of the pulp. The pulp which is. fed on to the wire. screen contains less than 1% fibre and" more .than 99% water; and until'most of thejwater. is removed from the paper, the paper is too weak to carry itself through the remaining water removal steps. It is, therefore, essential to remove the water as quickly as possible; and this is even more important with machines of increased speed.

In high speed Fourdrinier machines, the water is removed by means of suction boxes, the number of which may vary from a few to as many as a dozen or more. A suction box comprises a metal box with a perforated cover placed up against the the bottom of the wire screen over and in contact with which cover the wire screen is moved. A vacuum is maintained on the suction box, and the water is drawn into the boxes through the perforations in the cover. The greater the suction applied, the more water is removed, thereby permitting higher speeds or less further drying capacity.

The higher speed machines and the higher suction applied have introduced serious problems concerning the wear of the machine parts, due to the increased friction between the moving wire screen and the suction box cover. While slow machines operating at from 500 to 600 feet per minute will often have wires that wear for a period of months before they wear out or break, the 1200 to 1500 feet per minute machines used in making heavy kraft paper can wear out a wire screen in from three to five days. It is estimated that roughly 80% of the wire wear occurs due to the friction developed over the suction boxes. Wire screens are quite costly, but the biggest expense is incurred in the stoppage of the machines which is necessitated by changing the wire screens. It has been estimated that a wire change will cost, in wire, labor and loss of production, between ten to fifteen thousand dollars.

Many attempts. have been made, heretofore to im: prove the suction box covers so that mainly wire screen wear may be reduced but also so that the, operating life of the suction box cover may be long. Suction boxcovers generally in use today are made of end. grain maple. Some of this wood is wax impregnated to, produce some degree of lubrication, (to reduce, wire wear) and to stabilize. the wood against excessive, swell when wet; but such covers when notin use must be continuously kept Wet and are most often submerged in. water to prevent warpage or cracking of, the wood; Wood box covers of the most improved construction. have been designed to last about nine months on a high speed machine. On slow machines, resin impregnated paper or. cloth laminates, drilled for suction purposes, have been used;v but due to the higher friction between wire and'. resin laminate, the wire wears faster, although the laminate does not wear as fast aswool. Although the cost of screen wire and their change time are of paramount importance, the dual problem for high speed machines, is the, design of the suction box cover and use of materials therefor which yields the lowest frictional effects on the, moving wire and presents the most durable and most easily serv icing suction box cover.

I have found that the operatingor usefulflive's of both the Fourdrinier screen wire and the suction box cover are greatly increased by providing the. suction, box cover over. its screen wire contacting side with a body or sheet of a polytetrafluoroethylene (Teflon). surface. Teflon, possesses a. very low coefficient of, friction and; about one tenthof'that of wood, and I have found, that. its use as the contacting surface for thescreen wire results in a greatly l'owered'wire wear and thus in highly. reduced operating costs, on fast paper makingmachines. Teflon, however, possesses poor abrasion resistance and mars and cuts easily. Despite this, however, I have found that when used as the contacting surface of-the moving screen-wire, not only is the life ofthe moving screenwire greatly increased but that the lifefofthe 8. 1G- tion box cover, which wouldbe expectedto'be far less than that of the best of prior art covers, surprisingly equals or exceeds the same. Thus, I have found experimentally that Teflon topped suction boxes will even outlast the life of the best designed wood topped covers. The reasons for such unexpected and surprising results are not known unless it be the effect of the white water on the system in lubricating the wire over the Teflon surface.

To the accomplishment of these objects, my present invention relates to the novel suction box cover referred to and to a suction box cover as sought to be defined in the appended claims taken together with the following description and the accompanying drawings illustrating an embodiment thereof, in which:

Fig. 1 is a top plan view of the suction box cover of the present invention with part of the Teflon top broken away for illustrative purposes;

Fig. 2 is an end or transverse view thereof shown on an enlarged scale and taken partly in section in the plane of the line 2-2 of Fig. 1; and

Fig. 3 is a plan view of the same shown on a reduced scale and depicting the three component sections of which the cover may be made.

Referring now more in detail to the drawings, the suction box cover comprises in its broader aspects a perforated cover generally designated as C, said cover being provided over its top or screen wire contacting side with a body having a polytetrafluoroethylene (Teflon) surface.

In its more specific aspects, and in the preferred embodiment, the suction box cover comprises a base member 10, which may be made of metal or a resin laminated paper or cloth body to which is united a sheet of polytetrafiuoroethylene. In the drawings, I have illustrated the base as comprising a sheet of aluminum of thickness to which is united a sheet 12 of polytetrafiuoroethylene which may also be about /z thick, the Teflon sheet being adhered as by being cemented to the metal base at the contiguous faces 14 thereof.

The base member is employed as a support for the Teflon top sheet 12 which latter is flexible and should be supported planularly to prevent any concavity occurring on its top surface while under vacuum. The base member 10 is provided on its opposite sides with the metal runners 16 and 18, which may be secured to the base member along the length thereof by a plurality of screws such as 20, 20. These runners are used to build the box to an overall height of 1% so as to equal the height of prior art commercial wood covers.

The super-imposed Teflon and base laminae 12 and 10 are drilled to provide the suction perforations 22, 22, which latter are distributed transversely and longitudinally over substantially the entire length and width of the suction cover; and these may be drilled in suitable patern, such as illustrated in Fig. l of the drawings, it being understood that any desired pattern or style of drilled perforations may be used.

As illustrated both in Fig. 1 and Fig. 3, the suction box cover may be made in a plurality of sections, such as the two end sections 24 and 26, and the middle section 28, assembled together to form the suction box cover in the manner depicted in Fig. 1 of the drawings.

The structure of the improved suction box cover of the present invention, the function, use and advantages thereof, will in the main be fully apparent from the above detailed description. It will be further apparent that changes may be made in the design, arrangement, base materials and assembly of the parts without departing from the spirit of the invention and the scope thereof as defined in the following claims.

I claim:

1. A Suction box cover for Fourdrinier machines comprising a perforated cover for the suction box and in contact with which is moved the Fourdrinier screen wire, said cover comprising a base member and a screen wire contacting body consisting essentially of polytetrafluoroethylene on the base member.

2. A suction box cover fm- Fourdrinier machines comprising a perforated cover 'for the suction box and in contact with which is moved the Fourdrinier screen wire, said cover comprising ametal base attachable to the suction box and a screen wire contacting sheet consisting essentially of polytetrafiuoroethylene united to the base.

3. A suction box cover for Fourdrinier machines comprising a perforated cover for the suction box and in contact with which is moved the Fourdrinier screen wire, said cover comprising a resin laminated paper base attachable to the suction box and a screen wire contacting sheet consisting essentially of polytetrafluoroethylene united to the base.

4. A suction box cover for Fourdrinier machines comprising a perforated cover for the suction box and in contact with which is moved the Fourdrinier screen wire, said cover comprising a resin laminated cloth base attachable to the suction box and a screen Wire contacting sheet consisting essentially of polytetrafiuoroethylene united to the base. 1

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Pulp and Paper Manufacture, volume 3, McGraw-Hill Company, Inc., 1953. Library of Congress Card Cata logue Number 51-9649, pp. 107108. 

